Support RBM_ZERO_AND_CLEANUP_LOCK in ExtendBufferedRelTo(), add tests

For some reason I had not implemented RBM_ZERO_AND_CLEANUP_LOCK support in
ExtendBufferedRelTo(), likely thinking it not being reachable. But it is
reachable, e.g. when replaying a WAL record for a page in a relation that
subsequently is truncated (likely only reachable when doing crash recovery or
PITR, not during ongoing streaming replication).

As now all of the RBM_* modes are supported, remove assertions checking mode.

As we had no test coverage for this scenario, add a new TAP test. There's
plenty more that ought to be tested in this area...

Reported-by: Tom Lane <tgl@sss.pgh.pa.us>
Reported-by: Alexander Lakhin <exclusion@gmail.com>
Reviewed-by: Alexander Lakhin <exclusion@gmail.com>
Discussion: https://postgr.es/m/392271.1681238924%40sss.pgh.pa.us
Discussion: https://postgr.es/m/0b5eb82b-cb99-e0a4-b932-3dc60e2e3926@gmail.com

src/backend/storage/buffer/bufmgr.c

@@ -888,8 +888,6 @@ ExtendBufferedRelTo(ExtendBufferedWhat eb,
 	Assert((eb.rel != NULL) != (eb.smgr != NULL));
 	Assert(eb.smgr == NULL || eb.relpersistence != 0);
 	Assert(extend_to != InvalidBlockNumber && extend_to > 0);
-	Assert(mode == RBM_NORMAL || mode == RBM_ZERO_ON_ERROR ||
-		   mode == RBM_ZERO_AND_LOCK);
 
 	if (eb.smgr == NULL)
 	{
@@ -933,7 +931,13 @@ ExtendBufferedRelTo(ExtendBufferedWhat eb,
 	 */
 	current_size = smgrnblocks(eb.smgr, fork);
 
-	if (mode == RBM_ZERO_AND_LOCK)
+	/*
+	 * Since no-one else can be looking at the page contents yet, there is no
+	 * difference between an exclusive lock and a cleanup-strength lock. Note
+	 * that we pass the original mode to ReadBuffer_common() below, when
+	 * falling back to reading the buffer to a concurrent relation extension.
+	 */
+	if (mode == RBM_ZERO_AND_LOCK || mode == RBM_ZERO_AND_CLEANUP_LOCK)
 		flags |= EB_LOCK_TARGET;
 
 	while (current_size < extend_to)
@@ -1008,11 +1012,12 @@ ReadBuffer_common(SMgrRelation smgr, char relpersistence, ForkNumber forkNum,
 	{
 		uint32		flags = EB_SKIP_EXTENSION_LOCK;
 
-		Assert(mode == RBM_NORMAL ||
-			   mode == RBM_ZERO_AND_LOCK ||
-			   mode == RBM_ZERO_ON_ERROR);
-
-		if (mode == RBM_ZERO_AND_LOCK)
+		/*
+		 * Since no-one else can be looking at the page contents yet, there is
+		 * no difference between an exclusive lock and a cleanup-strength
+		 * lock.
+		 */
+		if (mode == RBM_ZERO_AND_LOCK || mode == RBM_ZERO_AND_CLEANUP_LOCK)
 			flags |= EB_LOCK_FIRST;
 
 		return ExtendBufferedRel(EB_SMGR(smgr, relpersistence),
@@ -1145,9 +1150,10 @@ ReadBuffer_common(SMgrRelation smgr, char relpersistence, ForkNumber forkNum,
 	}
 
 	/*
-	 * In RBM_ZERO_AND_LOCK mode, grab the buffer content lock before marking
-	 * the page as valid, to make sure that no other backend sees the zeroed
-	 * page before the caller has had a chance to initialize it.
+	 * In RBM_ZERO_AND_LOCK / RBM_ZERO_AND_CLEANUP_LOCK mode, grab the buffer
+	 * content lock before marking the page as valid, to make sure that no
+	 * other backend sees the zeroed page before the caller has had a chance
+	 * to initialize it.
 	 *
 	 * Since no-one else can be looking at the page contents yet, there is no
 	 * difference between an exclusive lock and a cleanup-strength lock. (Note

src/test/recovery/meson.build

@@ -41,6 +41,7 @@ tests += {
       't/033_replay_tsp_drops.pl',
       't/034_create_database.pl',
       't/035_standby_logical_decoding.pl',
+      't/036_truncated_dropped.pl',
     ],
   },
 }

src/test/recovery/t/036_truncated_dropped.pl

@@ -0,0 +1,136 @@
+# Copyright (c) 2021-2023, PostgreSQL Global Development Group
+
+# Tests recovery scenarios where the files are shorter than in the common
+# cases, e.g. due to replaying WAL records of a relation that was subsequently
+# truncated or dropped.
+
+use strict;
+use warnings;
+use PostgreSQL::Test::Cluster;
+use Test::More;
+
+my $node = PostgreSQL::Test::Cluster->new('n1');
+
+$node->init();
+
+# Disable autovacuum to guarantee VACUUM can remove rows / truncate relations
+$node->append_conf(
+	'postgresql.conf', qq[
+wal_level = 'replica'
+autovacuum = off
+]);
+
+$node->start();
+
+
+# Test: Replay replay of PRUNE records for a pre-existing, then dropped,
+# relation
+
+$node->safe_psql(
+	'postgres', qq[
+CREATE TABLE truncme(i int) WITH (fillfactor = 50);
+INSERT INTO truncme SELECT generate_series(1, 1000);
+UPDATE truncme SET i = 1;
+CHECKPOINT; -- ensure relation exists at start of recovery
+VACUUM truncme; -- generate prune records
+DROP TABLE truncme;
+]);
+
+$node->stop('immediate');
+
+ok($node->start(),
+	'replay of PRUNE records for a pre-existing, then dropped, relation');
+
+
+# Test: Replay of PRUNE records for a newly created, then dropped, relation
+
+$node->safe_psql(
+	'postgres', qq[
+CREATE TABLE truncme(i int) WITH (fillfactor = 50);
+INSERT INTO truncme SELECT generate_series(1, 1000);
+UPDATE truncme SET i = 1;
+VACUUM truncme; -- generate prune records
+DROP TABLE truncme;
+]);
+
+$node->stop('immediate');
+
+ok($node->start(),
+	'replay of PRUNE records for a newly created, then dropped, relation');
+
+
+# Test: Replay of PRUNE records affecting truncated block. With FPIs used for
+# PRUNE.
+
+$node->safe_psql(
+	'postgres', qq[
+CREATE TABLE truncme(i int) WITH (fillfactor = 50);
+INSERT INTO truncme SELECT generate_series(1, 1000);
+UPDATE truncme SET i = 1;
+CHECKPOINT; -- generate FPIs
+VACUUM truncme; -- generate prune records
+TRUNCATE truncme; -- make blocks non-existing
+INSERT INTO truncme SELECT generate_series(1, 10);
+]);
+
+$node->stop('immediate');
+
+ok($node->start(),
+	'replay of PRUNE records affecting truncated block (FPIs)');
+
+is($node->safe_psql('postgres', 'select count(*), sum(i) FROM truncme'),
+	'10|55', 'table contents as expected after recovery');
+$node->safe_psql('postgres', 'DROP TABLE truncme');
+
+
+# Test replay of PRUNE records for blocks that are later truncated. Without
+# FPIs used for PRUNE.
+
+$node->safe_psql(
+	'postgres', qq[
+CREATE TABLE truncme(i int) WITH (fillfactor = 50);
+INSERT INTO truncme SELECT generate_series(1, 1000);
+UPDATE truncme SET i = 1;
+VACUUM truncme; -- generate prune records
+TRUNCATE truncme; -- make blocks non-existing
+INSERT INTO truncme SELECT generate_series(1, 10);
+]);
+
+$node->stop('immediate');
+
+ok($node->start(),
+	'replay of PRUNE records affecting truncated block (no FPIs)');
+
+is($node->safe_psql('postgres', 'select count(*), sum(i) FROM truncme'),
+	'10|55', 'table contents as expected after recovery');
+$node->safe_psql('postgres', 'DROP TABLE truncme');
+
+
+# Test: Replay of partial truncation via VACUUM
+
+$node->safe_psql(
+	'postgres', qq[
+CREATE TABLE truncme(i int) WITH (fillfactor = 50);
+INSERT INTO truncme SELECT generate_series(1, 1000);
+UPDATE truncme SET i = i + 1;
+-- ensure a mix of pre/post truncation rows
+DELETE FROM truncme WHERE i > 500;
+
+VACUUM truncme; -- should truncate relation
+
+-- rows at TIDs that previously existed
+INSERT INTO truncme SELECT generate_series(1000, 1010);
+]);
+
+$node->stop('immediate');
+
+ok($node->start(), 'replay of partial truncation via VACUUM');
+
+is( $node->safe_psql(
+		'postgres', 'select count(*), sum(i), min(i), max(i) FROM truncme'),
+	'510|136304|2|1010',
+	'table contents as expected after recovery');
+$node->safe_psql('postgres', 'DROP TABLE truncme');
+
+
+done_testing();